The present invention relates to a power supply apparatus and methods of operation thereof, and more particularly, to uninterruptible power supplies (UPSs) and methods of operation thereof.
UPSs are commonly used to provide conditioned and/or auxiliary power to electronic equipment that provides critical functions, such as computer systems, telecommunications systems and medical equipment. Typically, UPSs can provide AC power from a backup source, such as a battery, generator or fuel cell, in the event that a utility power supply fails or becomes degraded.
UPSs may be coupled to and decoupled from one or more power sources using, for example, a relay. In particular, UPSs are often coupled to more than one source of power. For example, a UPS may have a primary source of power such as a utility, and a secondary source of power, such as battery or generator. The UPS may be coupled to the primary source of power and the secondary source of power using first and second relays, respectively. If one of the relays welds closed, the UPS may connect the sources together, which may damage the sources and/or interconnecting wiring.
Methods of determining a state of a relay have been developed to address this issue. For example, a light emitting diode (LED) may be placed across the relay contact to provide a visual indication as to whether the relay is open or closed. However, these types of sensors may not be reliable and may provide a false indication.